excellent ideas
the 3,000l aro tank i heated with 25m of thick walled alkathene in summer
had to watch it didn't heat too much though
winter would be a different proposition
tank will be half inside with polystyrene on outside
big acrylic windows inside
other tank will be 9m concrete construction
will look at solar heating systems ira
and the aqua therm
arapaima, stingrays and breeding reds would be nice